Polyuria is the increased formation and excretion of urine while polydipsia is increased thirst and water intake. Usually increased production of dilute urine results in a compensatory increase in water consumption, but the condition can be one of increased water intake resulting in the production of large volumes of dilute urine. While serious consequences are rare, excessive water intake and excessive urination can be early signs of some serious underlying conditions including Kidney failure, diabetes mellitus, uterine infection (called pyometra), liver disease, high blood calcium, uncommon abnormalities of the pituitary gland and inability of the tubules of the kidney to reabsorb water properly (i.e. "nephrogenic" diabetes insipidus).
Normal intake of water for a dog under normal conditions is about 90 ml per kilogram body weight per day while normal urine production is more than 45 ml of urine per kilogram body weight per day. Anything more than that, under normal environmental conditions, is considered polydipsia and polyuria respectively.
Besides increased thirst and increased urination, other symptoms will depend on underlying condition.